It is frequently necessary to burn gas at oil and gas installations. The gas is typically directed to a vertically standing pipe or flare stack. Gas exiting the top of the pipe is ignited with an ignitor. It is important that the gas be kept burning. With high winds, the flame can easily be blown out. As a result, high gas flow rates may be required to keep the flame burning externally of the flare stack. In addition, environmental concerns sometimes require that the burning of the flare gas be smokeless.
In one prior art flare tip, gas is vented through a central pipe. Steam and air is injected through smaller pipes that are parallel to the central pipe and disposed circumferentially around it. The smaller pipes extend beyond the end of the central pipe and blow steam at a 45.degree. angle towards the center of the central pipe. The injection of steam and air pushes oxygen into the gas stream from the central pipe and assists in ensuring complete combustion of the purge gas, such that the burn is smokeless. While this design is effective in avoiding smoke, it uses a lot of steam.
It is also known in the prior art of flare stacks to provide, at a flare tip, a central pipe within a concentric outer pipe, thus forming an annulus between them and to spread gas from the central pipe into the annulus along radially oriented horizontal tubes with openings in their top edges. Gas from the central pipe spreads out into the radial tubes and exits the openings. Air is blown into the annulus past the radial tubes to draw the gas upward and force a burn to take place above the top of the flare tip.
The inventor has found that the performance of flare tips in terms of wastage of steam may be improved by use of the invention described in the following.